This invention relates to charged particle energy analysers, particularly, though not exclusively, charged particle energy analysers having the capability to analyse simultaneously charged particles having a wide range of energies.
In charged particle optical systems various devices are available for analysing the spectrum of energies of beams of charged particles and these devices have been comprehensively described in various works on the subject of charged particle optics; see for example, xe2x80x9cPrinciples of Electron Opticsxe2x80x9d by P. H. Hawkes and E. Kasper (Academic Press, New York) 1989, and a paper by D. Roy and D. Tremblay, Rep Prog Phys. 53, 1621 (1990). In many applications, such as Auger electron spectroscopy of surfaces, the range of energies of interest in a single spectrum can cover more than an order of magnitude. The conventional way of obtaining such a spectrum has been to scan through the energy range using a single detector. A faster technique is to use a multidetector or series of detectors to cover an extended range of energies and then to scan the complete range of the spectrum either continuously or in steps. It seems that in all the known electrostatic charged particle energy analysers, with the exception of the hyperbolic field analyser, the range of energies that can be analysed at any one time is small, the ratio of the energy range to the mean energy being typically less than 0.1. Therefore, if the stepping method is used the required number of steps is at least of the order of 10.
It is clearly advantageous to be able to analyse the whole energy spectrum simultaneously. The hyperbolic field analyser described by M. Jacka, M. Kirk, M. El Gomati and M. Prutton in Rev. Sci. Instrum, 70, 2282 (1999) is able to do this. However, the hyperbolic field analyser has a substantially planar geometry and so suffers from the drawback that it is only able to analyse charged particles incident over a narrow angular range is azimuth.
According to a first aspect of the invention there is provided a charged particle energy analyser for analysing charged particles having a range of energies comprising, electrostatic focusing means having a longitudinal axis, a charged particle source for directing charged particles into an electrostatic focusing field generated, in use, by said electrostatic focusing means, and detection means for detecting charged particles focused by said electrostatic focusing means, wherein said electrostatic focusing field is defined by equipotentials which extend about said longitudinal axis over a predetermined range is azimuth and charged particles having different energies are brought to a focus by the electrostatic focusing field at different respective discrete positions.
Charged particle energy analysers according to this aspect of the invention have the capability to analyse simultaneously charged particles having a wide range of energies which are incident over the entire (360xc2x0) angular range in azimuth about the longitudinal axis or which are incident over one or more smaller azimuthal ranges. This combination of features enables the energy spectra of charged particles to be measured more rapidly than has been possible using known analysers, and also enables angular information to be obtained.
Charged particle energy analysers according to the invention may also be used in a second-order focusing mode whereby charged particles having a relatively narrow range of energies, but incident of a relatively wide angular range in elevation relative to the longitudinal axis can be focused.
According to another aspect of the invention there is provided a charged particle energy analyser for analysing charged particles comprising, electrostatic focusing means having a longitudinal axis, a charged particle source for directing charged particles into an electrostatic focusing field generated, in use, by said electrostatic focusing means, and detection means for detecting charged particles focused by said electrostatic focusing means, wherein said electrostatic focusing means is defined by equipotentials which extend about said longitudinal axis over a predetermined range in azimuth and said charged particle source directs said charged particles into said electrostatic focusing field over a predetermined angular range in elevation relative to said longitudinal axis, said predetermined angular range in elevation and/or the axial position of the charged particle source and/or the axial position of the electrostatic focusing field being set or adjustable for second-order focusing of charged particles.